1. Field of the Invention
The invention relates to a tooth system for transmitting a torque between two components disposed coaxially with one another, eg a shaft part and a hub part. The teeth have straight tooth surfaces, and root and tip fillet radii. Tooth systems of this type have been known for a long time and are the subject of German Standard DIN 5461 to 5465 and 5480.
These tooth systems are generally produced by hob milling, slotting or broaching. This machining enables solid components, in particular, to be manufactured very precisely. Frequently such a tooth system is also chosen for constructions in which the shaft part is solid, but the part on the hub side consists of several thin sheets of metal, for example in disc clutches, in which the discs have to be axially displaceable on the shaft during operation. Clutches of this type are also frequently disposed in the drive line of motor vehicles having an internal combustion engine. Special requirements with regard to accuracy and absence of noise are expected of these clutches because of the typical torsional vibration behavior of the motor.
2. Description of the Prior Art
The tooth system known from German Standard DIN 5461 has straight tooth surfaces, both on the shaft and on the hub, with the tooth surfaces being parallel to one another. In tooth systems comprising two parts which are not suppose to rest fixed on one another, such as, for example, a flange on a gear shaft, but are meant to remain axially movable, play is necessary in the tooth system. However as a result, after the play has been overcome, the two surfaces, which are only parallel in ideal circumstances, are one on top of the other under the torsion angle determined by play. Furthermore, as the two parts are constantly provided with the same pressure angles, contact only occurs at the edges or over a larger area in the case of corresponding deformation or when there is wear, particularly if the tooth system is manufactured with internal or external centering.
From German Standard DIN 5480 is known a tooth system having an involute profile with a trapezoidal reference profile, which produces an involute tooth surface during production in the hob milling process on the shaft part. With the hub part, which in the case of the disc clutch consists of thin discs, the blanking tool has to have a profile which exactly fits the shaft tooth. Even with this tooth system, which can also be produced for external, internal or surface centering, it is the edges that are important with the transmission of the torque to the one-sided support, subject to the necessary play stipulated by manufacture, because both the shaft and also the hub profiles have this same contour as stipulated in the standard. At the same time it should be borne in mind that these tooth systems, in contrast to a tooth system of gear wheels, has more and smaller teeth and receive a completely different tooth shape, in particular the inner tooth system of the hub part. Each tooth has small fillet radii at the root and tip. This requires an expensive and sensitive blanking tool, and nevertheless, the hub parts are only produced with large tolerances and disadvantageous deformation in the area of the cutting edges (blanking tool). Greater precision for both parts necessitates expensive machining and maintenance work. Too great a play in the coupling is the cause of unpleasant rattling noise and premature wear.
From French Patent Specification No. 1 560 270 is known a tooth system for the transmission of a torque. The tooth surfaces however do not have a flat surface, but consist of curves, with the root circle directly passing over into the tip circle. Between the hub and shaft parts only line contact can occur.
From German Auslegeschrift No. 26 36 382 is known a tooth system, in which the teeth consist of two surface parts under one angle, with there being no transition radius either at the tip or at the root or at the bend between the surface parts. With this tooth system there should intentionally occur no surface contact, but there should be line contact between the hub part and the shaft part.
In the U.S. Patent No. 2,969,250 to Kull, which issued on Jan. 24, 1961 is disclosed a tooth system, which likewise only has curved tooth surfaces and therefore only permits line contact.
These last mentioned citations relate in particular to hexagon heads of screws and therefore do not satisfy the requirements for shaft-hub connections regarding centering precision, surface bearing strength and resistance to wear.